Bacteria isolated from the digestive tracts of blue mussels (Mytilus edulis) contaminated with paralytic shellfish toxins (PSTs) were screened for the ability to reduce the toxicity of a PST mixture in vitro. Bacteria were isolated on marine agar and grown in marine broth supplemented with a mussel extract and an algal extract containing PSTs (saxitoxin, neosaxitoxin, gonyautoxins 2 and 3, decarbamoyl-gonyautoxins 2 and 3 and C1/C2 toxins). Toxin levels were measured before and after 5d of incubation, using high performance liquid chromatography (HPLC) and reduction of overall toxicity verified by mouse bioassays. Of the 73 bacterial cultures screened, seven isolates were designated "competent" PST degraders, individually reducing the overall toxicity of the PSTs by at least 90% within 3d. Most isolates degraded 100% of the saxitoxin and neosaxitoxin within 1-3d. In all cases, the overall kinetics of degradation of the toxicities was first order, as were the individual degradation kinetics of most of the individual toxins. This is the first report of nearly complete elimination of PSTs through bacterial action and may perhaps result in the development of a practical means to eliminate or reduce the risk of PSP intoxication associated with shellfish consumption.